Micro-electro-mechanical systems (“MEMS”) are currently employed in a variety of different applications. A few widely used applications for MEMS devices include scanned beam displays, scanned beam imagers, and scanned beam endoscopes.
A typical scanned beam display includes a MEMS die formed from a semiconductor substrate having a reflective scanner supported by torsion arms about which the scanner may rotate. In operation, an image may be generated by modulating light emitted from a light source (e.g., a light-emitting diode, a laser, etc.) and scanning the emitted light by rotating the scanner. Various optical components (e.g., lenses) may be used to modify the light before scanning, after scanning from the scanner, or both. For example, in a head-mounted display, a beam may be scanned through a viewer's pupil to generate the image on the viewer's retina.
In a scanned beam imager, a beam may be scanned across a field-of-view (“FOV”) and affected by the FOV, such as being reflected by an object to be imaged. The affected light may be collected and an image may be generated that is characteristic of the FOV.
In order to accurately generate the image, the rotational position of the reflective scanner should be accurately determined. In one conventional approach, the position of the scanner may be determined using photodetectors. Another conventional approach for determining the scanner position is by mounting resistive material on the torsion arms that changes resistance as the torsion arms are twisted. The change in resistance may be correlated with the position of the scanner. For comb-drive MEMS scanners, dedicated sensor-comb fingers different than the drive comb fingers may be provided. Capacitance between a fixed sensor comb fingers of the MEMS scan frame and the moving sensor-comb fingers may be determined. The rotational position of the scanner may be correlated to the measured capacitance. The aforementioned approaches typically rely on adding additional components to the system (e.g., photodetectors), additional electrical connections, requires separate components (e.g., the sensor comb fingers) that consume valuable space on a MEMS die, among other problems.